In general, an engine block of an internal combustion engine is composed of a plurality of split bodies such as a cylinder head, a cylinder block, and a crank case. Further, this engine block has securely fastened thereto, by means of bolts, various brackets such as engine mount brackets for fixing the internal combustion engine itself to a vehicle, brackets for fixing auxiliaries (a compressor for an air-conditioner, an alternator, and the like) for the internal combustion engine to the engine block, and the like.
For example, Japanese Patent Application Publication No. 2003-49706 (JP-A-2003-49706) discloses a structure in which an engine mount bracket is securely fastened to lateral walls of an upper block having cylinders formed therein and a lower block supporting a crankshaft, across the respective blocks.
In the engine block, which is composed of a plurality of split bodies as disclosed in Japanese Patent Application Publication No. 2003-49706 (JP-A-2003-49706), the following inconveniences are presumable in the case of a structure in which each bracket is securely fastened across both adjacent ones of the split bodies, namely, a first split body and a second split body.
For example, aluminum alloys are often used for engine blocks in recent years for the sake of weight saving. On the other hand, iron (cast iron or the like) is often used for brackets from the standpoints of cost, strength, and the like. In the case where the material for the engine block and the material for the brackets are different from each other as in this case, there is a difference in thermal expansion coefficient (linear expansion coefficient) between the respective materials. More specifically, the linear expansion coefficient of the brackets is smaller than the linear expansion coefficient of the cylinder head, the cylinder block, and the crank case, which constitute the engine block. Thus, the thermal contraction amount of the brackets is smaller than the thermal contraction amount of the respective component members of the engine block. For example, as shown in FIG. 5, under a low-temperature environment, a force resulting from the aforementioned difference in thermal contraction amount to hinder the contraction of a cylinder block 300 and a crank case 400 is directly applied from a bracket 500 to a first fastening portion 310 of the cylinder block 300 to which the bracket 500 is fastened and a second fastening portion 410 of the crank case 400 to which the bracket 500 is fastened. When the contraction of the cylinder block 300 around the first fastening portion 310 and the contraction of the crank case 400 around the second fastening portion 410 are hindered as described above, a difference in contraction amount is created with respect to other regions. Thus, under the low-temperature environment, mating faces C of the cylinder block 300 and the crank case 400, which are located between the first fastening portion 310 and the second fastening portion 410, open.
The opening of the mating faces as described above is a phenomenon that occurs when there is a difference in thermal expansion amount or thermal contraction amount between the split bodies constituting the engine block and the brackets. Accordingly, the opening of the mating faces may also be caused when the linear expansion coefficient of the brackets is larger than the linear expansion coefficient of the split bodies constituting the engine block, namely, when the thermal expansion amount of the brackets is larger than the thermal expansion amount of the split bodies. In this case, the respective split bodies are pulled by the brackets at high temperatures, and the mating faces of the split bodies open as a result. Further, even in the case where the linear expansion coefficient of the split bodies constituting the engine block and the linear expansion coefficient of the brackets are equal to each other, a difference in thermal expansion amount or thermal contraction amount is created between the split bodies and the brackets when there is a difference in temperature between the split bodies and the brackets. Therefore, the mating faces of the split bodies may open in a similar fashion.